Refactor IViewModelService

[rrickgauer]

• [x] GetCommunityPageViewModelAsync
• [x] GetJoinedCommunitiesPageViewModelAsync
• [x] GetPostPageViewModelAsync
• [x] GetCommentsApiResponseAsync
• [x] GetCommentApiResponseAsync

[rrickgauer]

Split up the ViewModelService into separate classes:

public interface IViewModelService<in TArgs, TViewModel>
{
    public Task<ServiceDataResponse<TViewModel>> GetViewModelAsync(TArgs args);
}